This invention deals with a coreless, miniature motor. In more detail, it deals with improvement of a miniature motor for use in assembly of pagers, mobile telephones and other portable electronic equipment, to serve as a vibration alarm device that rings by vibration.
Vibration alarm devices that ring by vibration instead of ringing by sound have been adopted as alarm devices to notify one of received messages in conferences and other locations where production of a sound is to be avoided.
Conventionally, vibration alarm devices of this sort have used coreless motors that rotate an eccentric weight.
Such a coreless motor has, as shown in FIG. 9, an external housing 1 that comprises a cylindrical case 1a and caps 1b and 1c that fit into both ends of the case 1a, a central rotating shaft 2 of which one end projects through the cap 1b at one end of the case 1a and the other end is located within the case 1a; the rotating shaft 2 is supported and free to turn within a bearing 3 in the cap 1b, and an eccentric weight 4, a stator 5 and a rotor 6 are assembled on the same axis as the rotating shaft 2.
Of these, the eccentric weight 4 is fixed on the end of the rotating shaft 2 that protrudes from the external housing 1 beyond the cap 1b. The stator 5 is fixed between a bearing 5a, which is on the same axis as the rotating shaft 2 and located towards its other (enclosed) end, and a ring 1d inside from the cap 1b through which the rotating shaft 2 is inserted; the stator 5 is an assembly of field magnets in the form of a hollow cylinder with the rotating shaft 2 as its central axis. The rotor 6 has a cylindrical coil 6a located, with intervening spaces, between the field magnets 5b and the case 1a of the external housing 1. The coil 6a is assembled so as to turn together with the rotating shaft 2, by means of support by a support plate 6b that is between the bearing 5a of the field magnets 5b and the other (enclosed) end of the rotating shaft 2.
In addition, there is a commutator 7 on the same axis between the support plate 6b of the coil 6a and the other (enclosed) end of the rotating shaft 2, as well as a brush mount (not illustrated) on the cap 1c for the brush 8, and a lead wire 9 that connects the brush 8 to a battery or other power source.
The eccentric weight 4 mounted on the axis that protrudes outside the external housing 1 of this coreless motor presents a major obstacle to efforts to make portable electronic equipment such as pagers and mobile telephones smaller and lighter. The external housing 1 is essential to the structure of the coreless motor described above, and in addition to the size of the external housing, a case must be formed between it and the coil 6a, so the external housing 1 is another obstacle to efforts to reduce size and weight. Moreover, because the eccentric weight 4 spins about with support on one side, the load of the spinning is particularly heavy on the bearing 3, and a loss of torque occurs. Moreover, if the equipment undergoes a fall or shock, the heaviness of the weight 4 can bend the rotating shaft 2; it is not possible to make the shaft 2 with a very small diameter.
In addition to the eccentric weight and the external housing discussed above, there are other problems with the structure of the brushes of the conventional coreless motor.
A round wire or ribbon wire that is straight or bent in a U-shape with the base welded to a brush holder is generally used as the brush. Two brushes are mounted so as to press like springs, from both sides, against the commutator 7 that is mounted on the same axis as the rotating shaft 2. Because of the overall length and the mounting, a large assembly space is required. Moreover, if the outer diameter of the commutator 7 is reduced along with that of the rotating shaft 2, it becomes difficult to adjust the pressure accurately and the length of the springs is no longer adequate, so this is not desirable as a brush for use with a miniature coreless motor.
The same sort of problems are manifest in the structure of a gyro motor. For this reason there is a desire for coreless miniature motors, including gyro motors, that meet the conditions of small size, light weight, excellent shock resistance, and good precision. There are limits, however, to motors that rotate with eccentric weights.
The purpose of this invention is to provide a coreless miniature motor, including vibrating coreless motors and gyro motors, with superior portability in terms of small size and light weight, that can function as a weight or flywheel that produces rotary vibration without relying on rotation of an eccentric weight supported on one side by a rotating shaft.
An additional purpose of this invention is to provide a coreless miniature motor that can be built without an external housing, and which costs less, is easily assembled and well-suited to mass production.
Moreover, it is a purpose of this invention to focus on the structure of brush attachment, and to provide a coreless miniature motor with small, high-performance brushes that have a fully effective length even when used with commutators of small diameter.
One more purpose is to provide a coreless miniature motor with superior shock resistance, and other features of this invention will become clear through the following detailed explanation.